CORE B: CLINICAL RESOURCES CORE The clinical spectrum of parkinsonian disorders is varied and may represent a continuum of inter-related phenotypes with common etiologic factors. While the diagnosis of the most common form, Parkinson disease (PD) may be relatively straightforward, discriminating PD from other variations of the phenotype can be challenging. Several forms of parkinsonism demonstrate extensive clinical overlap, which can interfere with accurate diagnosis. Since the power of genetic studies relies heavily on the accuracy of diagnoses, it is important that clinicians with special interest and training in movement disorders be involved in diagnosing patients for these studies. The differential diagnosis of PD includes many disorders that can mimic aspects of PD, including essential tremor; drug-induced parkinsonism; other secondary parkinsonian syndromes (vascular parkinsonism, tumors and other mass lesions of the basal ganglia); normal pressure hydrocephalus; and other atypical parkinsonian syndromes (Parkinson plus) including progressive supranuclear palsy (PSP), multiple system atrophy (MSA), cortical basal degeneration (CBD). Some of these conditions (such as essential tremor or REM Sleep Behavior disorder) may represent early manifestations of a disease process leading to parkinsonism or PD. Expert evaluation by a movement disorders specialist and post-mortem neuropathologic diagnosis enhances accurate diagnosis of participants in genetic studies. This core builds on the clinical assessment expertise developed over the previous twelve years. While the main goal of is to provide resources for Udall Center projects, the clinical data, DNA samples and tissue resources collected will benefit other Udall Centers and PD researchers as well. Specifically, the core will provide the following services: 1) Enroll new participants and collect samples on existing participants as needed to support biomarker studies; 2) Continue the longitudinal study of individuals with parkinsonism and unaffected controls participating in the tissue donation program; 3) Continue operating the Udall Center Brain Bank.